1. Field of the Invention
This invention pertains to the field of power transmission systems for motor vehicles especially to such systems that sense a speed difference between driveshafts, transmit power to the slower driveshaft alone, and allow the faster driveshaft to overrun.
2. Description of the Prior Art
In a conventional differential mechanism, either an interaxle differential or interwheel differential, if traction of the outputs is unequal, i.e., if friction contact with ground is less than required to maintain driving contact with ground, then maximum torque transmitted to ground is twice the torque that can be transmitted to the output having the lesser traction.
The gearless, interwheel differential described in U.S. Pat. No. 1,238,659 transmits power between an input shaft, connected to the differential by mating bevel gears, and to axleshafts directed perpendicular to the input shafts. The patent describes use of the differential to drive axleshafts through frictional contact between an input member, driven by the bevel gearset, and friction plates, fixed to the axleshafts and forced into frictional contact with the input member. When one axleshaft turns faster than the other, e. g., while the motor vehicle is turning, frictional contact between the input member and the friction plate connected to the faster axleshaft is removed by displacing driving balls to a position that reduces frictional contact pressure between the input and the faster axleshaft.
The disc differentials described in U.S. Pat. No. 2,060,558 and U.S. Pat. No. 2,179,923 include friction disc clutches for driveably connecting an input to the differential and two axleshafts, extending perpendicular to the differential input and directed away from the differential to the drive wheels of the vehicle. A coiled helical compression spring maintains frictional contact among the discs of the clutches. When the speed of one of the axleshafts increases with respect to the other, the friction clutch associated with the faster axleshaft is disengaged, thereby disconnecting that axleshaft from the input. In this condition, the slower axleshaft receives all the torque through its associated friction clutch from the differential input. Here again, as in U.S. Pat. No. 1,238,659, the differential is an interwheel differential, which transmits power transversely along the axleshafts perpendicular to the driving input
The positive clutch differential described in U.S. Pat. No. 4,400,996 is also an interwheel differential transmitting power from a longitudinally directed input bevel gear, through operation of positive friction clutches to transversely directed coaxial shafts directed perpendicular to the differential input. The axleshafts are connected by pressure rings having inclined friction surfaces to a casing, driven rotatably by a bevel pinion. The differential includes a balking ring to prevent immediate reengagement in the event one pressure ring becomes disengaged from the input when its associated axleshaft is overrunning with respect to the other axleshaft.